The invention relates to a type of voltage supplying apparatus specifically designed to use fuel cell as the voltage supplying source for the apparatus.
With the diminishing of global energy source and the rising of environmental protection, conventional energy sources such as gasoline and combustion are becoming more inadequate. Therefore, many researches have been focusing on the development of new energy sources, fuel cell being the main focus.
Emphasis has been put on fuel cell because of its unique features that are in tune with the modern trend for energy: efficiency, cleanness, and quietness. The efficiency of fuel cell system is extremely high, exceeding over 40% efficiency. Combine with cogeneration technique to recycle the heat produced from the reaction and fuel cell can achieve 80% efficiency. In term of cleanness, fuel cell does not produce any kind pollutants during the energy producing process, including voice pollution. Fuel cell can be applied to different fields including electricity, industry, transportation, space industry, and military. Application can be found in power plant, back-up battery, portable power supply, forklift, robot, electric cars, small submarine and even powers for space shuttles.
But fuel cell itself still has some problems, one of them being polarized dependency loss. Due to the inner chemical characteristic of fuel cells, when fuel cells are connected to a load, the voltage of the connected side is easy to alter with the load current. Also, the ratio of alteration can reach 50%. When the load current increases, the amount of change of the fuel cell also increases. Therefore, usually the direct output voltage of the fuel cell is not used. Instead, techniques of power electronics will be used first to stabilize output voltage from the fuel cell. Then, the stabilized voltage will be output for further use. For example, the technique of high frequency switching can be applied, using a DC-DC voltage converter to stabilize the voltage output by the fuel cell.
FIG. 1 demonstrates including a DC voltage supplying device 100, a DC-AC voltage converter, and an Auxiliary Battery 108. DC-AC voltage converter 206 can accept DC voltage supplied by DC voltage supplying device 100 or Auxiliary Battery 108. Then, it can convert the accepted DC voltage to AC output voltage 110. This AC output voltage 110 can be used on many applications, such as e-vehicles or household electricity supplies, etc.
Special attention should be paid that the voltage source output from DC voltage supplying device 100 is produced by a fuel cell 102. However, the voltage output from fuel cell 102 is not directly used as the output voltage for DC voltage supplying device. Intead, it has to be stabilized by a DC-DC voltage converter 104 before it can be used as the output voltage for DC voltage supplying device 100. Fuel cell 102 and DC-DC voltage converter 104 are connected in series. In other words, the output voltage from the fuel cell must be completely processed by the DC/DC converter before it can be output. Nevertheless, there are usually some energy losses when DC-DC voltage converter 104 is put to work. Therefore, when DC-DC voltage converter is stabilizing the output voltage from fuel cell 102, some part of the voltage energy is wasted, causing a decrease in efficiency.
Thus, in voltage supplying devices those use fuel cells as voltage sources, a circuit structure that can lower the energy losses is needed, in order to raise the efficiency of electrical energy used.